JP5570054B2 - Optical glass - Google Patents

Description

The present invention relates to an optical glass, and in particular, a composition suitable for molding and fine structure transfer, which has a high refractive index (n _d ), low dispersion and low yield point (At), and improved devitrification resistance during molding. It relates to an optical glass having

In recent years, aspherical lenses are increasingly used as optical devices are remarkably reduced in size and weight. This is because aspherical lenses can easily correct light aberration, reduce the number of lenses, and make the device compact.
An aspherical lens or the like is manufactured by heating and softening a glass preform and precision molding press molding it into a desired shape. There are two main methods for obtaining a preform. One is a method of cutting a glass piece from a glass block or bar, and the other is a preform process. The other is a glass melt dripped from the tip of a nozzle to form a spherical shape. This is a method for obtaining a glass preform.
In order to obtain a glass molded product by precision molding, it is necessary to perform pressure molding of the preform at a temperature in the vicinity of the yield point (At). For this reason, the higher the yield point (At) of the preform, the higher the temperature of the mold in contact with it, and the more the mold surface is oxidized and consumed, which necessitates maintenance of the mold. Mass production cannot be realized. For this reason, it is desired that the optical glass constituting the preform can be molded at a relatively low temperature, and therefore has a low glass transition point (Tg) and / or yield point (At).
On the other hand, as glass used for a mold lens, glass having various optical characteristics is required depending on its use, and among them, demand for glass having a high refractive index, low dispersion, and a low yield point is increasing.
As a conventional glass that satisfies the above optical characteristics, there is a barium flint type glass, but it contains not only PbO (lead oxide) harmful to the human body, but also metal lead precipitates on the surface of the product during precision press molding. There is a problem that the glass surface is likely to be rough due to fusion with the mold, which is not preferable.
Further, in a digital camera, it is necessary to reduce the surface reflection of the lens as much as possible, and an antireflection coating is used. However, in order to suppress the reflectance and the incident angle dependency and widen the wavelength range, a very multilayer coating film is required, and the process is complicated and expensive.
In order to achieve low reflectivity without the need for a coating film, it is known to form a microstructure smaller than the wavelength of light on the surface of a lens or the like. For example, efforts have been made by nanoimprinting using a resin. ing. A material having a low softening temperature such as a resin is relatively easy to mold with a finely processed mold, but the temperature dependence of the refractive index of the resin is about −1 × 10 ⁻⁴ (K), which is higher than that of glass. Since it is about two orders of magnitude larger, the change in the refractive index affects the image quality as the image quality becomes higher. Therefore, a glass for fine structure transfer has been studied in order to increase the functionality of optical components. The microstructure transfer glass is an ultra-precise mold press product obtained by transferring the concavo-convex shape of a mold of the order of μm to nm to the glass surface. For example, by replacing a conventional optical component with a lens having a fine structure, it is advantageous to increase the functionality, size and cost of the device. As for the characteristics required for glass, it is extremely important that the yield point is 500 ° C. or less in order to suppress the deterioration of the mold. Conventionally, the present invention can also be applied to Ni and P molds that have been used mainly for resin lens molding. Further, since the coating film is not applied as a lens, the weather resistance of the glass itself is also required.

As a glass having the above optical properties containing no ^{_{PbO, P 2 O 5 -R 1}} 2 O-R 2 O- ( rare earth oxide or the like) type glass (where ^{R 1:} an alkali metal ^{oxide, R} 2: 2 Valent metal oxides). This optical glass has a refractive index (n _d ) of 1.63 to 1.67, an Abbe number (ν _d ) of 47 to 59, and a yield point (At) of 500 ° C. or less (Patent Document 1).
The ^{_{P 2 O 5 -R 1 2 O}} -BaO-ZnO- ( high-valent oxide) type optical glass is disclosed. This optical glass has a refractive index (n _d ) of 1.52 to 1.7 and an Abbe number (ν _d ) of 42 to 70 (Patent Document 2).
The ^{_{P 2 O 5 -R 1 2 O}} -R 2 O-Nb 2 O 5 based ^{_{glass, P 2 O 5 -R 1 2}} O-Nb 2 O 5 -WO 3 based _glass, P ₂ O 5 ^-R _{1 2 O-Bi} 2 O ₃ based glass is disclosed. These optical glasses have a refractive index (n _d ) of 1.57 or more and a yield point (At) of 570 ° C. or less (Patent Documents 3 to 7).
The _{P 2 O 5 -B 2 O 3} -R 1 2 O-R 2 O-Gd 2 O 3 based _{glass, P 2 O 5 -B 2 O} 3 -R 1 2 O-BaO-ZnO -based glass is disclosed ing. These optical glasses have a refractive index (n _d ) of 1.54 or more and an Abbe number (ν _d ) of 57 or more (Patent Documents 8 and 9).
The ^{_{P 2 O 5 -R 1 2 O}} -R 2 O-ZnO-Al 2 O 3 based glass is disclosed. This optical glass has a refractive index (n _d ) of 1.55 to 1.65, an Abbe number (ν _d ) of 55 to 65, and a yield point of 500 ° C. or less (Patent Documents 10 to 12).
JP-A-11-139845 JP 2004-217513 A JP 2002-293572 A JP 2005-247659 A JP 2003-335549 A JP 2004-2153 A JP 2003-238197 A JP 2006-52119 A WO2003 / 072518 JP 2004-168593 A JP 2004-262703 A JP 2005-53749 A

However, the optical glasses disclosed in Patent Documents 1 and 2 have a high refractive index, low dispersion, and a low yield point. However, since the yield point is lowered with an alkali metal oxide, zinc oxide, or the like, the weather resistance is improved. Problems are likely to occur.
In addition, the optical glasses disclosed in Patent Documents 3 to 7 have high dispersion (ν _d ≦ 42), and there is a problem that they are not suitable for high refractive index and low dispersion applications.
Further, the optical glasses disclosed in Patent Documents 8 and 9 have a high refractive index and low dispersion, but since the yield point is a high temperature of 500 ° C. or higher, an undesirable problem is likely to occur on the mold surface.
In addition, since the optical glasses disclosed in Patent Documents 10 to 12 above contain Al ₂ O ₃ as an essential component for improving weather resistance, the melting temperature of the glass rises and the Pt crucible is likely to be eroded. Therefore, the problem that the transmittance is lowered on the low wavelength side is likely to occur.

  Therefore, the present invention solves the disadvantages of the above-mentioned conventional phosphate optical glass, and has a high refractive index (particularly preferably a refractive index of 1.6 or higher), low dispersion (Abbe number of 42 or higher), and a low yield point during molding. An object of the present invention is to provide an optical glass having improved devitrification resistance and suitable for molding such as precision mold press molding and transfer of a fine structure.

As a result of intensive studies to solve the above-mentioned problems, the present inventors set the composition within a specific range in glass production, specifically, P ₂ O ₅ —BaO—ZnO—Nb _2. It has been found that the above-mentioned problems can be solved by using an O ₅ glass as a basis, a combination of an alkali metal oxide and an appropriate amount of a rare earth oxide, and addition of fluoride. completed.
That is, the optical glass of the present _invention, P ₂ O 5: _25~50 wt%, BaO: 16 to 35 wt%, ZnO: 1 to 25 _weight, Nb ₂ O 5: _{3~10 wt%,} B 2 _{O 3} The first feature is that it is a P ₂ O ₅ —BaO—ZnO—Nb ₂ O ₅ -based glass containing : 0.1 to 8 wt% and F: 0.1 to 10 wt% .
The optical glass of the present invention, in addition to the first feature, _G eO 2: 0 to 8 _{wt%, Al} 2 O 3: _0~1 wt% (excluding 1 wt%), _Li 2 O : _0-8% by weight, Na 2 O: 0 _wt%, K 2 O: 0-8 wt%, CaO: 0 wt%, SrO: 0 to 15 wt%, MgO: 0 to 5 wt% , WO ₃ : 0 to 10 wt%, Gd ₂ O ₃ : 0 to 8 wt%, Ta ₂ O ₅ : 0 to 8 wt%, Y ₂ O ₃ : 0 to 5 wt%, ZrO ₂ : 0 to 3 wt% %, LiF: 0 wt%, NaF: 0 _wt%, ZnF 2: 0 to 15 _wt%, BaF 2: among 0-15 wt%, containing at least one or more components, all components The second feature is that it is configured to exclude the case where the content of is 0 .
The optical glass of the present invention, in addition to the first or second aspect, refractive index _{(n d)} from 1.58 to 1.70, an Abbe's number ([nu _d) is from 42 to 58, a glass transition point ( The third feature is that Tg) is 470 ° C. or lower and the glass yield point (At) is 500 ° C. or lower.
The optical glass of the present invention has a fourth feature that it is used for transferring a fine structure in addition to the features described in any one of the first to third aspects.
Here, the transfer of the fine structure means using a mold having a fine structure composed of irregularities having a period on the order of μm to nm on the surface, and transferring the fine structure on the surface of the mold to the surface of the optical glass. Say that. This is a fine structure transfer using a precision transfer method called a precision glass mold method or a nanoimprint method.

According to the optical glass of claim 1, since it has the composition shown therein, it is possible to provide an optical glass having high refractive index / low dispersion, low glass transition point, and low yield point characteristics. became. Further, it is possible to provide an optical glass suitable for mold molding such as precision mold press molding and fine structure transfer because the surface is hardly clouded during molding. Of course, it does not contain lead and is safe . It can increase the stability of the glass to further. Moreover, the meltability of glass and the weather resistance of glass can be improved.
According to the optical glass of Claim 2 , in addition to the effect by the structure of the said Claim 1, by containing the composition shown there, the high refractive index ( _nd ) as an optical characteristic of glass, Low dispersion can be promoted. Moreover, it is possible to obtain an optical glass having a low yield point and hardly causing white turbidity and suitable for molding such as precision mold press molding and transfer of a fine structure.
According to the optical glass of Claim 3 , in addition to the effect by the structure of Claim 1 or Claim 2 , the refractive index (n _d ) is 1.58 to 1.70, and the Abbe number (ν _d ) Is 42 to 58, the glass transition point (Tg) is 470 ° C. or less, and the glass yield point (At) is 500 ° C. or less. A material suitable for molding and fine structure transfer can be provided.
According to the optical glass of the fourth aspect , in addition to the effect of the structure according to any one of the first to third aspects, the optical glass has a period smaller than the wavelength of light, for example, by being used for transferring a fine structure. An optical glass such as a lens in which the fine structure of the two-dimensional concavo-convex structure is accurately transferred to the glass surface can be obtained. The optical glass having such a surface structure can exhibit very excellent performance for preventing reflection of light.

The components and their contents in the optical glass of the present invention will be described.
The component P ₂ O ₅ is a component for forming a glass network structure, and is an essential component for imparting stability that can be produced to glass.
P ₂ O ₅ causes the content 25 to 50 wt%. If it is less than 25% by weight, it becomes difficult to obtain a stable and good glass. On the other hand, if it exceeds 50% by weight, a material having a sufficiently high refractive index cannot be obtained.
The content of P ₂ O ₅ is more preferably 28 to 45% by weight in consideration of glass stability, refractive index, and the like.

The component BaO is essential for enhancing the stability of the glass and lowering the yield point and the liquidus temperature.
BaO is contained in an amount of 15 to 35% by weight. When BaO is less than 15% by weight, the yield point increases, which is not preferable from the viewpoint of glass stability. On the other hand, if it exceeds 35% by weight, a high refractive index cannot be maintained.
The content of BaO is more preferably 16 to 33% by weight in consideration of glass moldability, refractive index, and the like.

The component ZnO is essential for suppressing the occurrence of devitrification during glass molding and improving the moldability and stability of the glass.
ZnO is contained in an amount of 1 to 25% by weight. If it is less than 1% by weight, the effect is insufficient. On the other hand, if it exceeds 25% by weight, the liquidus temperature of the glass is raised, and the glass transition point and yield point are increased.
The content of ZnO is more preferably 3 to 23% by weight and optimally 3 to 20% by weight in consideration of glass moldability, stability, glass transition point, and yield point.

The component Nb ₂ O ₅ is essential as a component that contributes most to making the glass have a high refractive index.
Nb ₂ O ₅ is contained in an amount of 3 to 10% by weight. If it is less than 3% by weight, the effect of increasing the refractive index of the glass is insufficient. On the other hand, the content exceeding 10% by weight is not preferable because the stability of the glass is impaired.
The content of Nb ₂ O ₅ is more preferably 4 to 8% by weight in consideration of the refractive index and the stability of the glass.

Component B ₂ O ₃ is a component that forms a glass network structure and stabilizes the glass. It can be contained at 8% by weight or less as an optional component. If it exceeds 8% by weight, the refractive index decreases, which is not preferable.
The content of B ₂ O ₃ is preferably 0.1 to 8% by weight, more preferably 0.1 to 7% by weight, and most preferably 0.1 to 6% from the viewpoint of glass stabilization and refractive index. It is good to set it as weight%.

The component GeO _{2 is} also a component that forms a glass network structure and stabilizes the glass.
Addition of GeO ₂ is effective in increasing the refractive index and can satisfy a desired optical constant. It can be contained at 8% by weight or less as an optional component. If it exceeds 8% by weight, the stability of the glass is lowered, which is not preferable.
The content of GeO ₂ is preferably 1 to 7% by weight and optimally 1 to 6% by weight in view of increasing the refractive index and glass stability.

The component Al ₂ O ₃ is an effective component for suppressing the occurrence of devitrification during molding. It is also effective in weather resistance. It can be contained as an optional component in an amount of 1% by weight or less (excluding 1% by weight). If it is 1% by weight or more, the liquidus temperature of the glass is raised and the refractive index is lowered.
The content of Al ₂ O ₃ is preferably 0.1 to 0.9% by weight and optimally 0.5 to 0.8% by weight in consideration of the devitrification suppressing function and weather resistance. Good.

The component Li ₂ O is an effective component for lowering the glass transition point and at the same time maintaining a good refractive index. It can be contained at 8% by weight or less as an optional component. If it exceeds 8% by weight, the viscosity of the glass is lowered and the stability of the glass is impaired.
The content of Li ₂ O is preferably 0.1 to 8% by weight and optimally 1 to 7% by weight in consideration of the above functions.

The component Na ₂ O is also an effective component for reducing the glass transition point and at the same time maintaining a good refractive index. It can be contained at 10% by weight or less as an optional component. When it exceeds 10% by weight, the refractive index of the glass is lowered.
The content of Na ₂ O is preferably 0.1 to 10% by weight and optimally 1 to 8% by weight in consideration of the glass transition point and the refractive index.

Component K ₂ O is also an effective component for reducing the glass transition point and at the same time maintaining a good refractive index. It can be contained at 8% by weight or less as an optional component. If it exceeds 8% by weight, the refractive index of the glass is lowered.
The content of K ₂ O is preferably 0.1 to 8% by weight and optimally 1 to 7% by weight in consideration of the glass transition point and the refractive index.

The components Li ₂ O, Na ₂ O and K ₂ O are preferably contained in combination of two or more as an alkali metal oxide. Due to the mixed alkali effect, the glass transition point and the yield point are effective to be lowered while the glass can be manufactured with stability.
When used in combination, any two of these three components, or the total content of the three components, is preferably 1 to 10% by weight. More preferably, the content is 2 to 8% by weight.

Component CaO increases the stability of the glass and is effective in improving moldability. It can be contained at 10% by weight or less as an optional component. When it exceeds 10% by weight, the refractive index of the glass is lowered.
The content of CaO is preferably 0.1 to 10% by weight and optimally 1 to 8% by weight in consideration of glass stability, moldability, and refractive index.

The component SrO increases the stability of the glass and is effective for improving the moldability. It can be contained at 15% by weight or less as an optional component. When it exceeds 15% by weight, the refractive index of the glass is lowered.
The content of SrO is preferably 0.1 to 15% by weight and optimally 1 to 12% by weight in consideration of glass stability, moldability, and refractive index.

The component MgO increases the stability of the glass and is effective for improving the moldability. As an optional component, it can be contained at 5% by weight or less. If it exceeds 5% by weight, the refractive index of the glass is lowered.
The MgO content is preferably 0.1 to 5% by weight and optimally 1 to 4% by weight in consideration of glass stability, moldability, and refractive index.

The component WO ₃ is an effective component for providing a glass with a high refractive index and a formability with a low yield point. It can be contained at 10% by weight or less as an optional component. If it exceeds 10% by weight, the stability of the glass is impaired.
The content of WO ₃ is preferably 0.1 to 10% by weight and optimally 1 to 8% by weight in consideration of the glass refractive index, moldability, and glass stability.

The components Gd ₂ O ₃ , Ta ₂ O ₅ , Y ₂ O ₃ and ZrO ₂ are effective for increasing the refractive index and Abbe number of the glass.
Gd ₂ O ₃ and Ta ₂ O ₅ can each be contained in an amount of 8% by weight or less as optional components. If it exceeds 8% by weight, the stability of the glass is impaired.
The preferable contents of Gd ₂ O ₃ and Ta ₂ O ₅ are 0.5 to 8% by weight, respectively, and optimally 1 to 7% by weight.
Y ₂ O ₃ can be contained at 5 wt% or less as an optional component. If it exceeds 5% by weight, the stability of the glass is impaired.
The content of Y ₂ O ₃ is preferably 0.1 to 5% by weight.
ZrO ₂ is an optional component, but can be contained at 3% by weight or less. If it exceeds 3% by weight, the stability of the glass is impaired.
The content of ZrO ₂ is preferably 0.1 to ₂ % by weight.

The components LiF, NaF, ZnF ₂ and BaF ₂ are effective for increasing the melting property of the glass, lowering the yield point and the liquidus temperature, and improving the weather resistance of the glass.
LiF and NaF can each be contained at 10 wt% or less as optional components. If it exceeds 10% by weight, the stability of the glass is impaired.
The preferable contents of LiF and NaF are 0.5 to 10% by weight, respectively, and optimally 1 to 8% by weight.
ZnF ₂ and BaF ₂ can be contained as optional components in an amount of 15% by weight or less. If it exceeds 15% by weight, the stability of the glass is impaired.
The preferable contents of ZnF ₂ and BaF ₂ are 0.5 to 15% by weight, respectively, and optimally 1 to 13% by weight.

F contained in the glass is an effective component for enhancing the melting property of the glass and the weather resistance of the glass. As an optional component, it can be added at 10% by weight or less. If it exceeds 10% by weight, the stability of the glass is impaired.
The content of F is preferably 0.1 to 10% by weight, and more preferably 0.1 to 8% by weight in consideration of the meltability of glass, the weather resistance of glass, and the stability of glass.

Yb ₂ O ₃ is preferably not included because it has a strong absorption band in the region of 950 to 1000 nm.
Bi ₂ O ₃ is effective for lowering the yield point of the glass when contained, but if it is contained in a large amount, it has a problem that the glass tends to be colored. When Bi ₂ O ₃ is contained, the content is 5% by weight or less.

Regarding the raw material for producing optical glass in the embodiment, for example, for component P ₂ O ₅ , LiPO ₃ , NaPO ₃ , KPO ₃ , Al (PO ₃ ) ₃ , Ba (PO ₃ ) _2, etc. can be used. In addition, for component B ₂ O ₃ , H ₃ BO ₃ , B ₂ O _{3 and the} like can be used, and other components such as various oxides, carbonates, nitrates and the like which are usually used as raw materials are also used. Glass raw materials can be used.
Using the above raw materials in the component range described above, melting at 900-1300 ° C., homogenizing through each step of clarification (gas removal) and stirring, then pouring into a mold and cooling slowly. Thus, the optical glass of the present invention can be obtained which is colorless, has a high refractive index, a low yield point, is transparent, is homogeneous, and has excellent workability.

The following (1), (2), and (3) are specific examples of a very preferable composition as an optical glass that solves the problems of the present invention and has a high refractive index, low dispersion, and a low yield point. . These optical glasses are also excellent in chemical durability.
₍₁₎ B 2 _{O 3} is 0.1-3 _wt%, P 2 _{O 5} is 30-36 wt%, Li ₂ O is 1-6 wt%, Na ₂ O 1 to 5 wt%, BaO 28 35 wt%, ZnO 10 to 15 wt%, ZnF ₂ is 0.5-4 wt%, _Gd 2 _{O 3} 0.5 to 5 wt%, _Nb 2 _{O 5} is 5 to 10 wt%, Ta ₂ Glass in which O ₅ is 0.5 to 3% by weight.
₍₂₎ B _{2 O 3} is 0.1-3 _wt%, P 2 _{O 5} is 30-36 wt%, Li ₂ O is 1-6 wt%, Na ₂ O 1 to 5 wt%, BaO 28 35 wt%, ZnO 10 to 15 wt%, ZnF ₂ is 0.5-4 wt%, _Gd 2 _{O 3} 0.5 to 5 wt%, _Nb 2 _{O 5} is 5 to 10 wt%, Ta ₂ A glass comprising 0.1 to 3% by weight of O _{5 and} 0.1 to 3% by weight of ZrO ₂ .
₍₃₎ B 2 _{O 3} is 0.1-3 _wt%, P 2 _{O 5} is 30-36 wt%, Li ₂ O is 1-6 wt%, Na ₂ O 1 to 5 wt%, BaO 28 35 wt%, ZnO 10 to 15 wt%, ZnF ₂ is 0.5-4 wt%, _Gd 2 _{O 3} 0.5 to 5 wt%, _Nb 2 _{O 5} is 5 to 10 wt%, ZrO ₂ Glass consisting of 0.1 to 3% by weight.

The present invention will be further described below with reference to examples. However, the present invention is not limited to these examples.
Here, examples 1～8,12～15,22 in reference example of the present invention not containing _B 2 _{O 3} and / or F, Example 9～11,16～21 is in the embodiment of the present invention is there.
The raw materials were prepared and mixed so as to have the component compositions of Examples 1 to 22 and Comparative Examples 1 to 5 shown in Tables 1 to 4, and these were put in a platinum crucible, and 900 ° C. to 1300 in an electric furnace. The glass was melted at 0 ° C., then poured into a mold and gradually cooled to obtain an optical glass.
About each obtained optical glass, the refractive index ( _nd ), Abbe number ((nu) _d ), the glass transition point (Tg), and the yield point (At) were measured. The presence or absence of defects such as cloudiness was confirmed with a microscope.
Next, each glass plate was cut into a square shape to obtain a plurality of cut pieces having the same dimensions. Furthermore, the molding surface of the plurality of cut pieces was mirror-polished, and the washed sample was used as a glass preform for press molding.
This molding glass preform is put into a press molding machine having an upper core and a lower core provided with a noble metal release film, and up to a temperature near the yield point (At) in N ₂ gas or vacuum atmosphere. After heating, pressurization was performed by press forming, and after cooling, the product was taken out as a press-formed product. Observation (appearance) on the molding surface of this press-molded product and observation of the core surface in contact with glass (core surface) were performed. When fogging occurs on the core surface, it is due to component volatilization from the glass, indicating that minute roughness is generated on the press-molded surface.

  Comparative Example 1 has the same composition as the glass described in Example 14 of Patent Document 1. Comparative Example 2 has the same composition as the glass described in Example 1-3 of Patent Document 2. Comparative Example 3 has the same structure as the glass described in Example 1 of Patent Document 3. Comparative Example 4 has the same composition as the glass described in Example 2 of Patent Document 8. Comparative Example 5 has the same composition as the glass described in Example 1 of Patent Document 9.

In Examples and Comparative Examples, the refractive index (n _d ) and Abbe number (ν _d ) were measured using a refractometer (KPR-200, manufactured by Kalnew).
The glass transition point (Tg) and the yield point (At) are measured by heating a rod-shaped sample having a length of 15 to 20 mm and a diameter (side) of 3 to 5 mm at a constant rate of 5 ° C. while increasing the sample elongation. And the thermal expansion curve obtained by measuring the temperature.
For evaluation of weather resistance, the obtained glass was processed into about 10 × 10 × thickness 2 mm, and both surfaces of 10 × 10 were mirror-polished. The polished glass was held in a constant temperature and humidity chamber at about 65 ° C. and a humidity of 90%, and the surface state was observed at regular intervals, and evaluation was performed based on the time during which the glass surface was clouded and spots were observed.
The measurement results are shown in Tables 1 to 4.

As is apparent from Tables 1 to 3, the glasses of the examples of the present invention all have a high refractive index (n _d ) of 1.58 or more, while having a high Abbe number (ν _d ), and as an optical glass It has a sufficient optical constant. Further, the occurrence of cloudiness on the molding surface during molding was sufficiently suppressed.
These results indicate that the optical glass of the present invention has properties suitable for enabling mass production.
In addition, any glass of the examples of the present invention is easily formed because the yield point (At) is within a relatively low temperature range of 500 ° C. or less. From these things, it turns out that the glass of this invention is a glass suitable for precision mold press molding.
On the other hand, the glasses of Comparative Examples 1 and 2 were subjected to a weather resistance test, and as a result, fogging began to occur on the surface within 50 hours. All of the glasses of Comparative Examples 3 to 5 have a high yield point (At) and a large deterioration of the mold surface.

  The optical glass of the present invention has a high refractive index, a high Abbe number, a low glass transition temperature and a low yield point, hardly causes white turbidity during precision mold press molding, has excellent devitrification resistance, and is particularly suitable for molding aspherical lenses and the like. As an optical glass suitable for mass production, it has industrial applicability.

Claims (4)

P ₂ O _5: 25~50 wt%, BaO: 16 to 35 wt%, ZnO: 1 to 25 _{wt%, Nb} 2 O 5: _{3~10 wt%,} B ₂ O 3: 0.1~8 wt% , F: 0.1 to 10 optical glass, which is a _{P 2 O 5 -BaO-ZnO-} Nb 2 O 5 based glass containing by weight%. GeO _2: 0 to 8 _{wt%, Al} 2 O 3: _0~1 wt% (excluding 1 _wt%), Li 2 O: 0~8 _wt%, Na 2 O: 0 wt%, K ₂ O: 0 to 8 wt%, CaO: 0 wt%, SrO: 0 to 15 wt%, MgO: 0 to 5 _wt%, WO 3: _{0~10 wt%, Gd} 2 O 3: 0~8 _{wt%, Ta} 2 O 5: _{0~8 wt%, Y} 2 O 3: _{0~5 wt%,} ZrO 2: 0 to 3 wt%, LiF: 0 wt%, NaF: 0 wt%, Of ZnF ₂ : 0 to 15% by weight, BaF ₂ : 0 to 15% by weight, at least one component is contained, and the constitution is such that the content of all components is 0. The optical glass according to claim 1. Refractive index (n _d ) is 1.58 to 1.70, Abbe number (ν _d ) is 42 to 58, glass transition point (Tg) is 470 ° C. or lower, and glass yield point (At) is 500 ° C. or lower. The optical glass according to claim 1 or 2. The optical glass according to claim 1, wherein the optical glass is used for transferring a fine structure .